The present invention relates to an improved control system for a converter of the type comprising a three-phase current generator driven by a direct current motor.
Converters of this type are utilized to supply current to loads, which may, for example, be motors to drive compressors and ventilators of the air-conditioning systems provided in the cars of a d.c. operated subway or intracity trains. In such use it is desirable to maintain the voltage and frequency of the three-phase current network supplied by the generator within the tolerances for which the loads are designed even if the direct voltage supplied to the motor rises, for example, by 25% with respect to its rated value or drops by 30%. Moreover, with a symmetrical load on the d.c. network, the voltages between any two phase lines at the output of the generator preferably should not deviate significantly from one another, i.e., the voltage differences, for example, should be no greater than .+-. 1%.